This dataset is a collection of imagery of Nikunau Island coral reef systems. They are pairs of imagery where one image was acquired during a suspected bleaching event. The second is a control image taken at some point prior to the event. The images are co-located and radiometrically calibrated for comparison. The difference images are analyzed for evidence of bleaching.
Additional information on methodology can be found here: <http://www.ngdc.noaa.gov/dmsp/coral/methodology.html>